Heretofore, an energy storage device capable of being charged-discharged such as a secondary battery is known. This energy storage device includes an electrode assembly, a case that houses the electrode assembly along with electrolyte solution, an external terminal that is mounted on the case, and a current collector that is disposed in the case and connected to the electrode assembly. As shown in FIG. 6, this type of energy storage device may include a conduction member 105 that makes an external terminal 103 and the current collector 104 conductive, and a conduction member cutting mechanism 106, in addition to the electrode assembly 101, the case 102, and the current collector 104 (see JP-A-7-245090). In such an energy storage device, the conduction member cutting mechanism 106 has a cutting part 107. When the internal pressure of the case 102 rises up to predetermined pressure, the cutting part 107 is lifted, and an edge 107a of the cutting part 107 cuts the conduction member 105.
In the energy storage device 100 having the above configuration, overcharge or overvoltage caused by charging or the like raises the internal pressure of the case due to gas generated by the decomposition of electrolyte solution and the like. Then, when the internal pressure rises up to a predetermined value, the conduction member cutting mechanism 106 cuts the conduction member 105. Consequently, the energy storage device 100 stops the supply of current from the outside to the electrode assembly 101. As a result, the generation of gas in the case 102 is reduced, and a rise in internal pressure due to the generation of the gas is reduced. Thus, the generation of the gas is suppressed, so that rupture, explosion, and the like of the case is prevented, and the electrolyte solution and the like can be prevented from being released outside the case.
In the energy storage device 100, in an abnormal case where the internal pressure of the case 102 rises by an influence of overcharge, overvoltage, or the like, cutting of the conduction member 105 decouples an energization path that has been allowing conduction from the external terminal 103 to the electrode assembly 101. Accordingly, in the above energy storage device 100, the energization path is decoupled in the abnormal case, and therefore electric power stored in the electrode assembly 101 cannot be discharged to the outside.